Process for producing potassium hydroxide

Abstract

A process for producing potassium hydroxide by electrolysis of potassium chloride in an electrolytic cell comprising an anode compartment and a cathode compartment partitioned by a cation exchange membrane, which process comprises supplying potassium chloride to the anode compartment for the electrolysis to form potassium hydroxide in the cathode compartment, characterized in that said cation exchange membrane is a multi-layer membrane comprising at least two layers including a main layer made of a perfluorocarbon polymer having carboxylic acid groups as its ion exchange groups with an ion exchange capacity of from 0.9 to 1.6 meq/g dry resin and having a thickness of from 80 to 300 μm and a sulfonic acid film surface layer on the anode compartment side, made of a perfluorocarbon polymer having sulfonic acid groups as its ion exchange groups with an ion exchange capacity of from 0.5 to 1.5 meq/g dry resin and having a thickness of from 5 to 50 μm.

We claim: 
     
       1. A process for producing potassium hydroxide by electrolysis of potassium chloride in an electrolytic cell comprising an anode compartment and a cathode compartment partitioned by a cation exchange membrane, which process comprises: supplying potassium chloride to the anode compartment for the electrolysis which forms potassium hydroxide in the cathode compartment, said cation exchange membrane being a multi-layer membrane comprising at least three layers including a main layer formed of a perfluorocarbon polymer having carboxylic acid groups as its ion exchange groups with an ion exchange capacity of from 0.9 to 1.6 meq/g dry resin and having a thickness of from 80 to 300 μm, a sulfonic acid film surface layer on the anode compartment side formed of a perfluorocarbon polymer having sulfonic acid groups as its ion exchange groups with an ion exchange capacity of from 0.5 to 1.5 meq/g dry resin and having a thickness of from 5 to 50 μm, and a composite film layer interposed therebetween which is formed of a perfluorocarbon polymer having both carboxylic acid and sulfonic acid groups and having a thickness of from 5 to 50 μm.   
     
     
       2. The process according to claim 1, wherein the composite film layer is made of a blend comprising a perfluorocarbon polymer having carboxylic acid groups as its ion exchange groups and a perfluorocarbon polymer having sulfonic acid groups as its ion exchange groups. 
     
     
       3. The process according to claim 1, wherein the composite film layer is made of a blend comprising a perfluorocarbon polymer constituting the main layer and a perfluorocarbon polymer constituting the sulfonic acid film surface layer. 
     
     
       4. The process according to claim 3, wherein the composite film layer is made of a blend comprising 100 parts by weight of a perfluorocarbon polymer having carboxylic acid groups as its ion exchange groups and from 25 to 400 parts by weight of a perfluorocarbon polymer having sulfonic acid groups as its ion exchange groups.